The field of the present invention is bone repair and replacement. More specifically, the invention relates to a self-hardening, porous calcium phosphate composition, which has desirable handling characteristics and mechanical properties.
Naturally-occurring bone is comprised of both organic and inorganic components. The organic component includes growth factors, cartilage, collagen, and other proteins. The inorganic bone component includes non-stoichiometric, poorly crystalline apatitic (PCA) calcium phosphate, having a Ca/P ratio between 1.45 and 1.75 (Besic et al. (1969) J. Dental Res. 48(1):131). This inorganic bone mineral is continuously resorbed and regenerated in vivo by osteoclasts and osteoblasts in a process known as remodeling.
Bone implants are often used to augment the natural regeneration process in the event of bone defects and injuries. These implants must be biocompatible, capable of manipulation by a surgeon prior to implantation, and of a strength and composition such that the implant will maintain its shape in vivo.
Given its regenerative capabilities, natural bone is a potential implant material. However, the use of autogenic, allogenic, and xenogeneic bone is complicated by associated disease transmission, immunogenic implant rejection, patient morbidity, and complicated surgical procedures. Thus, synthetic bone implant materials have become the focus of increasing attention.
Moldable, self-setting calcium phosphate cements exhibit good strength properties and can be easily formed in situ to fill a range of clinical defects, but are remodeled slowly because cells cannot penetrate the dense material. Porous calcium phosphate ceramics are preferred as an implant material because they allow the penetration of blood vessels, cells and tissues, and drugs, which are important for promoting bone formation and preventing infection. When used as an implant material, porous calcium phosphate ceramics preferably have a high porosity. This high porosity can lead to lower mechanical strength in the porous bodies, thus negating their benefit as bone implants, which require high mechanical strength. Additionally, preformed porous blocks and granules can be difficult to manipulate and implant, and can lead to incomplete defect fill. Thus, there is a need for porous calcium phosphate ceramics having both excellent biocompatibility and mechanical strength.